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The angles of a triangle are $x, 2 x$ and $3 x$ . Find the exterior angle at the vertex whose interior angle is $2 x$ .

Class 9Exterior Angle of a TriangleGeometry — Lines and Angles

A120°
B90°
C150°
D60°

Step-by-Step Solution

x + 2 x + 3 x = 180

° gives

x = 30

°, so

2 x = 60

° and the exterior angle there is 120°. It also equals

x + 3 x = 120

°.

Answer: A) 120°

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